1. Field of the Invention
The present invention relates to diffusion barriers, and more particularly, to improved diffusion barriers for use with high dielectric constant materials.
2. Description of the Related Art
High dielectric constant materials (∈r greater than  greater than ∈SiO2=3.9∈0) have been widely studied as a replacement for silicon dioxide (SiO2) and silicon nitride (Si3N4) in silicon-based electronic devices, such as capacitors in dynamic random access memories (DRAMs), radio frequency (RF) circuits, metal-oxide-metal (MOM) capacitors, and metal-oxide-silicon (MOS) transistors. (See, e.g., P. K. Roy and I. C. Kizilyalli, xe2x80x9cStacked High-∈ Gate Dielectric for Gigascale Integration of Metal-Oxide-Semiconductor Technologies,xe2x80x9d Applied Physics Letters, Vol. 72, No. 22, pp. 2835-2837 (Jun. 1, 1988), and I. C. Kizilyalli, et al., xe2x80x9cMOS Transistors with Stacked SiO2xe2x80x94Ta2O5xe2x80x94SiO2 Gate Dielectrics for Giga-Scale Integration of CMOS Technologies,xe2x80x9d IEEE Electron Device Letters, Vol. 19, No. 11, pp. 423-425 (November 1998), both of which are incorporated by reference herein).
In particular, tantalum pentoxide (Ta2O5) has been proposed as an alternative to SiO2 with the advantage that it can be deposited by a low-temperature process ( less than 500xc2x0 C.). Generally, when manufacturing electronic devices incorporating Ta2O5, it may be advantageous to provide a titanium nitride (TiN) layer adjacent to the Ta2O5, for example, as a diffusion barrier or electrode, to form a Ta2O5/TiN structure. For example, a MOM capacitor could be formed from a layered stack of Al/TiN/Ta2O5/TiN/Ti. Likewise, a gate structure for an MOS transistor could be formed from a layered stack of Al/TiN/Ta2O5/SiO2/Si. It should be understood that many variations of the foregoing MOM capacitor and MOS transistor structures are well known in the art and the foregoing structures are meant to be illustrative and not limiting.
One problem associated with Ta2O5/TiN structures is that oxygen tends to migrate from the otherwise stable Ta2O5 and diffuse into the TiN during heat treatments, especially in cases where the TiN is Ti-rich. In the case of Ta2O5/TiN/Ti structures, such as in a MOM capacitor, the oxygen diffuses into the Ti. This diffusion of oxygen tends to reduce the Ta2O5 to elemental metal Ta. It has been found that this oxygen diffusion and reduction of Ta2O5 can occur at temperatures as low as 400-600xc2x0 C. This can be a serious problem when manufacturing electronic devices incorporating Ta2O5/TiN and Ta2O5/TiN/Ti structures as the resulting devices will have high leakage currents or will otherwise be inadequate or, in extreme cases, inoperable.
Accordingly, the present invention is directed to a diffusion barrier that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
Additional features and advantages of the invention will be set forth in the description that follows and, in part, will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the diffusion barrier and method particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purposes of the invention, as embodied and broadly described, the invention provides an electronic device comprising a titanium nitride layer, a high dielectric constant material, and a diffusion barrier disposed between the titanium nitride layer and the high dielectric constant material to prevent the diffusion of oxygen from the high dielectric constant material to the titanium nitride layer.
To further achieve these and other advantages and in accordance with the purposes of the invention, as embodied and broadly described, the invention also provides a metal-oxide-metal capacitor comprising a first interconnect layer, a first titanium nitride layer adjacent to the first interconnect layer, a first diffusion barrier adjacent to the first titanium nitride layer, a tantalum pentoxide layer adjacent to the first diffusion barrier, a second diffusion barrier adjacent to the tantalum pentoxide layer, a second titanium nitride layer adjacent to the second diffusion barrier, and a second interconnect layer adjacent to the second titanium nitride layer, wherein the first diffusion barrier prevents the diffusion of oxygen from the tantalum pentoxide layer into the first titanium nitride layer and the first titanium layer, and wherein the second diffusion barrier prevents the diffusion of oxygen from the tantalum pentoxide layer into the second titanium nitride layer.
To still further achieve these and other advantages and in accordance with the purposes of the invention, as embodied and broadly described, the invention also provides a metal-oxide-semiconductor transistor having a gate structure, the gate structure comprising an interconnect layer, a titanium nitride layer adjacent to the interconnect layer, a diffusion barrier adjacent to the titanium nitride layer, a tantalum pentoxide layer adjacent to the diffusion barrier, and a gate insulator adjacent to the tantalum pentoxide layer, wherein the diffusion barrier prevents the diffusion of oxygen from the tantalum pentoxide layer into the titanium nitride layer.
To still even further achieve these and other advantages and in accordance with the purposes of the invention, as embodied and broadly described, the invention also provides a diffusion barrier for preventing the diffusion of oxygen from a high dielectric constant material to a titanium nitride layer, the diffusion barrier comprising one or more layers, wherein each of the one or more layers comprises a material selected from the group consisting of metal carbide, metal nitride, metal boride, metal carbo-nitride, and silicon carbide.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.